The proposed work falls into four parts, all dealing with differentiation during the developmental biogenesis of intracellular membranes. The four test systems to be used are: a) the possible differential appearance of thylakoid membrane proteins during the light period of synchronous Chlamydomonas reinhardtii cells, when the cells and the chloroplast increase in mass some 4- to 6-fold; b) the possible arising of rat liver Golgi membrane proteins from precursor endoplasmic reticulum membrane proteins during secretion by the hepatic parenchyma cells; c) the possible differential synthesis of different proteins or sub-units of the rat liver endoplasmic reticulum membrane protein, cytochrome P450, during the perinatal period in the rat, at a time when the first spectral evidence for the protein appears; d) the differentiation of various regions of axonal membranes, such as post-synaptic and pre-synaptic membranes and synaptic vesicle membranes during the immediate post-natal period of the rat. The first three projects are a continuation of work already done and successful completion of these projects will lead to a fuller understanding of membrane organization and of the relationship of various intracellular membranes. The last project is a new one with regards to membrane or cell type, but it is hoped that previous methods and criteria used with regards to other membranes and other cells can be successfully applied here. In all cases, the biochemical assays will include enzymatic assays, gel electrophoresis, radioactive labeling and protein purification, all combined when necessary with electron microscopy.